Axial compression behaviour of small square tubes filled with self-compacting concrete: effect of L/B ratio

The focus of this study was investigating the effect of the unsupported length-to-width (L/B) ratio on the axial compressive behaviour of square self-compacting concrete-filled steel tube (SSCFT) specimens with small cross-sectional dimensions. SSCFT specimens with three different cross-sectional dimensions (25 mm × 25 mm, 30 mm × 30 mm and 35 mm × 35 mm) and L/B ratios of 2–12 were tested under axial compression. The compressive failure modes of the SSCFT specimens were observed and documented. The performance of SSCFT specimens was compared with that of square unfilled steel tube (SUT) specimens of identical cross-sectional dimensions in terms of the percentage increase in axial load capacity and concrete enhancement factor. The experimental findings revealed that steel tubes effectively confined the infill concrete. The SUT and SSCFT specimens with lower L/B ratios (≤4) predominantly exhibited local buckling failure, while those with higher L/B ratios (≥6) exhibited global buckling failure. The SSCFT specimens demonstrated a 20–40% increase in compressive strength and exhibited significantly higher resistance to buckling compared with the respective SUT specimens.